Battery-assisted backscatter RFID transponder

ABSTRACT

A radio frequency transponder includes at least one battery, which is coupled to provide electrical power for operating the transponder and at least one antenna, which is configured to receive and backscatter RF interrogation radiation from an interrogation device. An integrated circuit is arranged to store a code including information and, powered only with energy provided by the battery, to vary a radiation characteristic of the antenna responsively to the code so as to modulate the information onto the backscattered radiation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication 60/584,141, filed Jul. 1, 2004, of U.S. Provisional PatentApplication 60/602,342, filed Aug. 18, 2004, of U.S. Provisional PatentApplication 60/608,118, filed Sep. 9, 2004, of U.S. Provisional PatentApplication 60/614,552, filed Oct. 1, 2004, and of U.S. ProvisionalPatent Application 60/649,561, filed Feb. 4, 2005. These relatedapplications are assigned to the assignee of the present patentapplication, and their disclosures are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to radio frequencyidentification (RFID) systems, and particularly to battery-assistedbackscatter RFID transponders, their components and methods forproducing RFID transponders.

BACKGROUND OF THE INVENTION

Radio frequency identification (RFID) systems are used in a variety ofapplications, ranging from warehouse inventory control and containertracking, through automatic toll payment, to automatic supermarketcashier applications. In a typical RFID system, an RF transponder isattached to, or incorporated into, a tracked object. RF transmissionsbetween an interrogation device or a reader and the transponder are usedfor identifying or controlling the object, reading data, writing data orotherwise communicating with the transponder.

SUMMARY OF THE INVENTION

RF transponders are commonly classified in terms of the use they make ofan internal power source. A passive transponder has no internal powersource and uses the energy of the RF radiation transmitted by the reader(referred to herein as interrogation radiation) for powering thetransponder circuitry and for transmitting response radiation back tothe reader. (The response radiation typically comprises information,such as an identification number, transmitted from the transponder tothe reader.) An active transponder comprises an internal power sourcethat is used for both powering the transponder and for generating the RFenergy required for transmitting the response radiation. Abattery-assisted transponder (also referred to as a semi-active or asemi-passive transponder) comprises an internal power source. The energyof the response radiation is derived from the interrogation radiationprovided by the reader, and the transponder circuitry is powered by theinternal power source. Some battery-assisted transponders, referred toas backscatter transponders, generate the response radiation bybackscattering the interrogation radiation from the transponder antenna.Backscatter transponders typically transmit information to the reader bymodulating the backscattered radiation.

Battery-assisted backscatter transponders, as described in thebackground art, can use part of the energy of the received interrogationradiation for powering the transponder circuitry, in parallel to theirinternal battery. This configuration reduces the amount of energy thatis available for backscattering, thus reducing the achievablecommunication range of the transponder.

Embodiments of the present invention provide improved battery-assistedbackscatter RF transponder configurations that maximize the achievablecommunication range and extend the lifetime of the internal powersource. Exemplary performance measurements of such transponders invarious challenging test environments are shown hereinbelow.

In some embodiments, an integrated circuit (IC) in the transpondermodulates the information to be transmitted to the reader onto thebackscattered radiation using backscatter modulation. The IC modulates aradar cross-section (RCS) of the transponder antenna by varying theimpedance at the feed-point of the antenna. In particular, when anextreme mismatch, such as an open circuit, is introduced at the antennafeed-point, the energy of the interrogation radiation available forbackscattering is maximized, thus maximizing the communication range ofthe transponder.

In some embodiments, the antenna and the IC are jointly optimized so asto maximize the impedance mismatch at the antenna feed-point, and hencemaximize the achievable communication range. Additionally oralternatively, a modulation depth (denoted ΔRCS) defined as the ratiobetween the different RCS values is also maximized.

The RF transponders described herein can operate under variousprotocols, such as, but not limited to various transponder-talks-first(TTF) and reader-talks-first (RTF) protocols. Such protocols typicallydefine the different modes of operation for the transponder. In someembodiments, an energy saving (battery saving) module in the ICactivates and deactivates parts of the transponder responsively to theoperational modes defined in the protocol, in order to reduce the energyconsumption from the internal power source. In some embodiments, theenergy saving module controls the operational modes of the transponderresponsively to predetermined timeout conditions, to further reduceenergy consumption.

Embodiments of the present invention also provide improved methods forproducing RF transponders. In some embodiments, the power source of thetransponder is a thin and flexible battery that is printed on the samesubstrate as the IC and the antenna, as part of the transponderproduction process.

There is therefore provided, in accordance with an embodiment of thepresent invention, a radio frequency (RF) transponder, including:

-   -   at least one battery, which is coupled to provide electrical        power for operating the transponder;    -   at least one antenna, which is configured to receive and        backscatter RF interrogation radiation from an interrogation        device; and    -   an integrated circuit (IC), which is arranged to store a code        including information and, powered only with energy provided by        the battery, to vary a radiation characteristic of the antenna        responsively to the code so as to modulate the information onto        the backscattered_radiation.

In some embodiments, the transponder includes a substrate having atleast one of the IC, the at least one antenna and the at least onebattery disposed thereon.

In a disclosed embodiment, the at least one battery includes at least aprinted anode layer, a printed electrolyte layer and a printed cathodelayer disposed in at least one of a co-planar and a co-facialconfiguration. The electrolyte layer is disposed between the anode layerand the cathode layer. In another embodiment, the substrate is flexible.

In yet another embodiment, the transponder has a thickness no greaterthan 1 mm and a bending radius no greater than 25 mm.

In an embodiment, the transponder is attached to an object and at leastpart of the information in the IC is related to the object. Additionallyor alternatively, the transponder is adapted to be attached around acorner of an object so that the at least one battery is oriented in afirst plane and the at least one antenna is oriented in a second planedifferent from the first plane.

In another embodiment, the at least one antenna is selected from thegroup consisting of at least one of a monopole, a bent monopole, adipole, a bent dipole, a patch, an array antenna and a combinationthereof. Additionally or alternatively, the at least one antenna isconfigured to receive and backscatter the interrogation radiation in oneof an ultra-high frequency (UHF) range and a microwave frequency range.Further additionally or alternatively, the at least one antenna isarranged to receive and backscatter transverse electromagnetic (TEM)radiation.

In yet another embodiment, the at least one antenna includes afeed-point, the radiation characteristic includes a radar cross-section(RCS) of the at least one antenna, and the IC is arranged to vary a loadimpedance at the feed-point of the at least one antenna so as to varythe RCS of the at least one antenna between two or more different RCSvalues. In still another embodiment, the IC includes a solid-stateswitch operatively coupled to the feed-point of the at least oneantenna, which is arranged to switch the load impedance between a firstimpedance and a second impedance, responsively to a binaryrepresentation of the code.

In an embodiment, the IC is arranged to introduce a low resistive loadcondition at the feed-point of the at least one antenna so as tomaximize at least one of the two or more RCS values, thereby maximizinga communication range of the transponder. Additionally or alternatively,the IC is arranged to maximize a modulation depth defined as a ratiobetween two of the two or more RCS values. Further additionally oralternatively, the at least one antenna and the IC are arranged tojointly maximize the modulation depth and a communication range of thetransponder.

In an embodiment, the interrogation radiation received by the at leastone antenna has a first power level, and the at least one antenna andthe IC are arranged to backscatter the interrogation radiation at asecond power level that is greater than 75% of the first power level. Inanother embodiment, the second power level is greater than 95% of thefirst power level.

In still another embodiment, the IC is configured to comply with anoperation protocol defining two or more operational modes. Additionallyor alternatively, the IC includes an energy saving module, which isarranged to activate and deactivate parts of the transponderresponsively to the operational modes so as to reduce an energyconsumption from the at least one battery. In yet another embodiment,the protocol includes at least one of a transponder-talks-first (TTF)and a reader-talks-first (RTF) protocol.

In an embodiment, the protocol includes the RTF protocol, and the IC isconfigured to analyze signals carried by the interrogation radiation, toprogressively activate components of the transponder responsively to theanalyzed signals so as to reduce an energy consumption from the at leastone battery, to assess a relevance of the interrogation radiation to thetransponder based on the analyzed signals, and to enable the transponderto react to the interrogation radiation based on the relevance.Additionally or alternatively, the IC is arranged to evaluate one ormore timeout conditions and to deactivate predetermined components ofthe transponder responsively to the timeout conditions after havingdetected a presence of the interrogation radiation.

In another embodiment, the IC includes a battery status indicator, whichis configured to indicate an availability of sufficient electrical powerfrom the at least one battery, and the IC is configured to drawelectrical power from the interrogation radiation responsively to areported unavailability of sufficient battery power as determined by thebattery status indicator.

In yet another embodiment, the transponder includes at least one sensor,and the IC is arranged to receive an indication of a local condition ina vicinity of the transponder from the at least one sensor.

In still another embodiment, the transponder includes an energyconversion circuit, which is arranged to draw excess power from theinterrogation radiation, when the excess power is available, and toperform at least one of powering the IC and charging the at least onebattery using the drawn excess power.

In an embodiment, the IC is arranged to decode and react tointerrogation data carried by the interrogation radiation, theinterrogation data including at least one of a command relating to anoperation of the transponder and input data to be written to thetransponder.

There is also provided, in accordance with an embodiment of the presentinvention, a radio frequency (RF) transponder, including:

-   -   a battery, which is coupled to provide electrical power for        operating the transponder;    -   an antenna, which is arranged to receive and backscatter RF        interrogation radiation from an interrogation device;    -   an integrated circuit (IC), which is arranged to store a code        including information and, powered with energy provided by the        battery, to vary a radiation characteristic of the antenna        responsively to the code so as to modulate the information onto        the backscattered interrogation radiation; and    -   a substrate, on which the battery, IC and antenna are disposed,        and which is adapted to be fixed around a corner of an object so        that the battery is oriented in a first plane and the antenna is        oriented in a second plane different from the first plane.

There is further provided, in accordance with an embodiment of thepresent invention, a radio frequency (RF) transponder, including:

-   -   an antenna, which is arranged to receive interrogation radiation        at a first power level from an interrogation device and to        backscatter the interrogation radiation at a second power level        that is greater than 75% of the first power level; and    -   an integrated circuit (IC), which is arranged to store a code        including information and to vary a radiation characteristic of        the antenna responsively to the code so as to modulate the        information onto the backscattered radiation.

In an embodiment, the second power level is greater than 95% of thefirst power level.

There is additionally provided, in accordance with an embodiment of thepresent invention, a radio frequency (RF) transponder, including:

-   -   an antenna, which is arranged to receive first RF radiation        carrying signals from an interrogation device and to transmit        second RF radiation responsively to the first RF radiation;    -   a battery, which is coupled to provide electrical power for        operating the transponder; and    -   an integrated circuit (IC), which is operative in accordance        with a reader-talks-first (RTF) protocol, and which is        configured to detect a presence of the first RF radiation, to        analyze the signals carried by the first RF radiation, to        progressively activate components of the transponder        responsively to the analyzed signals so as to reduce an energy        consumption from the battery, to assess a relevance of the first        RF radiation to the transponder based on the analyzed signals,        and to enable the transponder to transmit the second RF        radiation based on the relevance.

In an embodiment, the IC is configured to assess the relevance of thefirst RF radiation by performing at least one of detecting a pattern inthe first RF radiation and determining addressing information in thefirst RF radiation. In another embodiment, the IC is arranged,responsively to the relevance of the first RF radiation, to perform atleast one of rejecting RF radiation not generated by an RF reader andrejecting RF radiation not addressed to the transponder.

There is also provided, in accordance with an embodiment of the presentinvention, a method for transmitting information from a radio frequency(RF) transponder, including:

-   -   providing a battery for operating the transponder;    -   configuring an antenna to backscatter RF interrogation radiation        that is transmitted from an interrogation device; and    -   varying a radiation characteristic of the antenna responsively        to the information so as to modulate the information onto the        backscattered radiation. The energy used to vary the radiation        characteristic is not derived from the interrogation radiation.

In an embodiment, providing the battery includes applying a printedbattery to a substrate having at least one of the IC and the antennadisposed thereon. In another embodiment, the battery is no greater than1 mm thick.

In yet another embodiment, the battery includes a flexible thin-layeropen liquid-state electrochemical cell including a first layer ofinsoluble negative electrode, a second layer of insoluble positiveelectrode and a third layer of aqueous electrolyte, the third layerbeing disposed between the first and second layers and including:

-   -   (a) a deliquescent material for keeping the open cell wet at all        times;    -   (b) an electroactive soluble material for obtaining required        ionic conductivity; and    -   (c) a water-soluble polymer for obtaining a required viscosity        for adhering the first and second layers to the third layer.

There is additionally provided, in accordance with an embodiment of thepresent invention, a method for manufacturing a radio frequency (RF)transponder, including:

-   -   providing a battery for operating the transponder;    -   configuring an antenna to backscatter RF interrogation radiation        that is transmitted from an interrogation device;    -   disposing the antenna and the battery on a substrate, wherein        the substrate is configured to allow for application of the        transponder around a corner of an object, so that the battery is        oriented in a first plane and the antenna is oriented in a        second plane different from the first plane.

There is further provided, in accordance with an embodiment of thepresent invention, a method for transmitting information from a radiofrequency (RF) transponder, including:

-   -   configuring an antenna to receive an interrogation radiation at        a first power level from an interrogation device and to        backscatter the interrogation radiation at a second power level        that is greater than 75% of the first power level;    -   storing a code including the information; and    -   varying a radiation characteristic of the antenna responsively        to the code so as to modulate the information onto the        backscattered radiation.

In an embodiment, the second power level is greater than 95% of thefirst power level.

There is additionally provided, in accordance with an embodiment of thepresent invention, a method for manufacturing a radio frequency (RF)transponder, including:

-   -   providing a substrate;    -   applying on the substrate an antenna suitable for backscattering        radio-frequency (RF) radiation;    -   applying an integrated circuit (IC) to the substrate, and        coupling the IC to vary a radiation characteristic of the        antenna so as to modulate information onto the backscattered        radiation; and    -   printing a battery on the surface of the substrate, so as to        provide electrical power for powering the transponder.

In an embodiment, printing the battery includes printing one or morebattery layers in at least one of a co-facial configuration and aco-planar configuration using respective inks including battery layermaterials. In another embodiment, the layer material includes at leastone of zinc, manganese dioxide (MnO₂) and zinc chloride (ZnCl₂).

In yet another embodiment, printing the battery includes:

-   -   forming a first battery assembly including:    -   i. printing a first electrode layer on the surface of the        substrate;    -   ii. applying an electrolyte on the first electrode layer; and    -   iii. applying a separator layer on the electrolyte of the first        electrode layer;    -   forming a second battery assembly including:    -   i. printing a second electrode layer of opposite polarity to the        first electrode layer on a second substrate; and    -   ii. applying the electrolyte on the second electrode layer; and    -   joining together the first battery assembly and second battery        assembly so that the layers are stacked and the electrolyte of        the second electrode layer is in co-facial contact with the        separator layer.

In still another embodiment, applying the antenna includes printing theantenna on the substrate. In another embodiment, the IC includes anorganic polymer IC and applying the IC includes using a printingtechnique to apply the IC. Additionally or alternatively, applying theantenna and the IC and printing the battery include printing a fullyprintable transponder.

There is also provided, in accordance with an embodiment of the presentinvention, a method for reducing energy consumption from a battery in aradio-frequency (RF) transponder operating in accordance with areader-talks-first (RTF) protocol, including:

-   -   detecting a presence of RF radiation at the transponder;    -   analyzing signals carried by the detected RF radiation;    -   progressively activating components of the transponder        responsively to the analyzed signals, so as to reduce the energy        consumption;    -   assessing a relevance of the RF radiation to the transponder        based on the analyzed signals; and    -   based on the relevance, enabling the transponder to react to the        RF radiation.

There is further provided, in accordance with an embodiment of thepresent invention, a radio-frequency identification (RFID) system,including:

-   -   at least one interrogation device, which is configured to        transmit RF interrogation radiation to RF transponders and to        receive and decode backscatter-modulated radiation from the RF        transponders responsively to the interrogation radiation;    -   at least one radio frequency (RF) transponder, including:    -   i. at least one battery, which is coupled to provide electrical        power for operating the transponder;    -   ii. at least one antenna, which is arranged to receive and        backscatter the interrogation radiation from the at least one        interrogation device; and    -   iii. an integrated circuit (IC), which is arranged to store a        code including information and, powered only with energy        provided by the battery, to vary a radiation characteristic of        the antenna responsively to the code so as to modulate the        information onto the backscattered radiation; and    -   at least one data processing device for processing data decoded        by the at least one interrogation device from the backscattered        modulated radiation.

There is additionally provided, in accordance with an embodiment of thepresent invention, an antenna for transmitting information from a radiofrequency (RF) transponder. The antenna is configured to receive RFinterrogation radiation at a first power level from an interrogationdevice, to backscatter the interrogation radiation at a second powerlevel that is greater than 75% of the first power level, and the antennahas a variable radiation characteristic, which is controllable by thetransponder so as to modulate the information onto the backscatteredradiation. In an embodiment, the second power level is greater than 95%of the first power level.

There is also provided, in accordance with an embodiment of the presentinvention, an energy saving circuit for reducing energy consumption froma battery in a radio-frequency (RF) transponder, including:

-   -   a state machine, which is arranged to detect a presence of RF        radiation at the transponder, to analyze signals carried by the        detected RF radiation, to progressively activate components of        the transponder responsively to the analyzed signals, so as to        reduce the energy consumption, to assess a relevance of the RF        radiation to the transponder based on the analyzed signals, and,        based on the relevance, to enable the transponder to react to        the RF radiation; and    -   one or more timeout circuits, which are arranged to evaluate        timeout conditions so as to activate predetermined components of        the transponder responsively to the analyzed signals.

There is further provided, in accordance with an embodiment of thepresent invention, a radio frequency (RF) transponder, including:

-   -   at least one battery, which is coupled to provide electrical        power for operating the transponder;    -   at least one antenna, which is configured to receive and        backscatter RF interrogation radiation from an interrogation        device; and    -   an integrated circuit (IC), which is arranged to store a code        including information and, powered with at least one of energy        provided by the battery and excess power from the interrogation        radiation, to vary a radiation characteristic of the antenna        responsively to the code so as to modulate the information onto        the backscattered radiation.

The present invention will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic pictorial illustration of an RFID system, inaccordance with an embodiment of the present invention.

FIG. 2 is a block diagram that schematically illustrates an RFID system,in accordance with an embodiment of the present invention.

FIGS. 3A and 3B are geometrical diagrams that schematically illustrateRFID transponder antennas, in accordance with embodiments of the presentinvention.

FIG. 3C is a schematic pictorial illustration of an RFID tag that isfolded over an edge of an object, in accordance with an embodiment ofthe present invention.

FIG. 4A is a diagram that schematically illustrates a radiation patternof an RFID transponder antenna, in accordance with an embodiment of thepresent invention.

FIG. 4B is a graph that schematically illustrates coverage of an RFIDtransponder antenna, in accordance with an embodiment of the presentinvention.

FIGS. 5A-5C are graphs that schematically illustrate backscatter valuesof RFID transponder antennas, in accordance with embodiments of thepresent invention.

FIGS. 6A and 6B are flow charts that schematically illustrate methodsfor communicating between a reader and an RFID transponder, inaccordance with embodiments of the present invention.

FIG. 7 is a state diagram that schematically illustrates energy savingoperation in reader-talks-first mode, in accordance with an embodimentof the present invention.

FIG. 8 is a schematic exploded view of an RFID transponder, inaccordance with an embodiment of the present invention.

FIG. 9 is a flow chart that schematically illustrates a method forproducing an RFID transponder, in accordance with an embodiment of thepresent invention.

FIG. 10A is a schematic exploded view of a printed battery, inaccordance with an embodiment of the present invention.

FIG. 10B is a flow chart that schematically illustrates a method forproducing a printed battery for a transponder, in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS System Description

FIG. 1 is a diagram that pictorially illustrates an RFID system 20, inaccordance with an embodiment of the present invention. System 20 inthis example, which is no way limiting is a warehouse inventory trackingsystem, in which objects, such as packages 24 are stored and tracked ina warehouse. An RF transponder 28, typically in the form of a tag orlabel, is attached to or is integrally formed with each package 24. Theterm “transponder” as used herein includes, but is not limited to,transponder forms such as tags, labels, stickers, wristbands, smartcards, disks or coins, glass transponders, plastic housing transponders,watch face transponders and any combination thereof. The term includesany size, thickness, shape, and form of transponder device. The termincludes integrated and non-integrated devices, such as, but not limitedto, devices integrated into the packaging of an object or integratedinto the object or product itself. The term includes transponders, madeby any suitable technology, including, but not limited to a printingtechnology.

A code comprising information relating to package 24 and/or totransponder 28 can be generated and stored in a memory of transponder28. Generally speaking, the code comprises any information that is to betransmitted from transponder 28 to reader 32. For example, theinformation may comprise an ID number that identifies package 24.Additionally or alternatively, the code may comprise data measured bysensors coupled to the transponder, or any other data that should betransmitted to reader 32.

An interrogation device, such as a reader 32, transmits interrogation RFradiation to transponder 28 in order to query its information.Typically, the interrogation radiation comprises a transverseelectromagnetic (TEM) wave. The interrogation radiation may compriseinterrogation data transmitted to the transponder, such as anidentification of the reader or an identification of the queriedtransponder. The transponder receives the interrogation radiation andresponds by modulating its code onto a backscattered response RFradiation, using methods, which will be explained in detail below. Thereader receives the backscattered radiation and demodulates the codesent by the transponder. The information in the code can be transmittedto a processing unit 36. In some embodiments, at least one repeater 42can be used for communicating between reader 32 and processing unit 36,for example in installations where there is no line of sight between thereader and the processing unit.

In the example of FIG. 1, a forklift is seen entering the warehousecarrying a new package 24 to be stored. Reader 32, in this exampleconfigured as a gate reader, interrogates transponder 28 attached topackage 24 in order to automatically update an inventory databasemaintained by processing unit 36 with the newly-arriving package.

The configuration shown in FIG. 1 is an exemplary RFID application,chosen purely for the sake of conceptual clarity. System 20 may compriseany other RFID system, in which RFID transponders are coupled to trackedobjects. System 20 may comprise, for example, a container trackingsystem, an automatic toll payment system, a book tracking system in alibrary, an airport baggage tracking system, an automatic cashier in asupermarket, animal tagging, human tracking such as, but not limited tobaby tracking in a hospital or armed forces tracking, supply chainmanagement, access control, asset control, total asset visibility,licensing, product handshaking, logistics management, movement and theftalarms. System 20 of the present invention can be used to monitorassets, packages, containers, and pallets when they are in warehousesand stockyards, as well as when they are in transit.

System 20 typically comprises multiple transponders 28 and may comprisemultiple readers 24 and/or multiple processing units. Reader 32 andtransponder 28 may communicate using any suitable protocol. An exemplaryprotocol is defined in an EPCglobal specification entitled “Class-1Generation-2 UHF RFID Conformance Requirements Specification v.1.0.2,”which is available atwww.epcglobalinc.org/standards_technology/specifications.html. Anotherexemplary protocol is the ISO 18000-6:2004 standard entitled “RadioFrequency Identification for Item Management—Part 6: Parameters for AirInterface Communications at 860 MHz to 960 MHz,” published by theInternational Organization for Standardization (ISO). The ISO/IEC18000-6:2004 standard is available at www.iso.org.

The modes of operation of transponder 28 and the functionality of eachmode can be defined in accordance with any suitable protocol, standardor interoperability interface, such as the EPCglobal and ISOspecifications cited above.

In some embodiments, system 20 may comprise multiple readers 32. Themultiple readers may be synchronized or non-synchronized. The multiplereaders may be connected to a single processing unit 36 or to multipleprocessing units. Interrogation radiation from more than one reader maycause mutual interference problems. In some embodiments, readers 32 ofsystem 20 can use a “listen before talk” protocol in order to avoid themutual interference. Additionally or alternatively, readers 32 can usesynchronized or non-synchronized frequency hopping for minimizinginterference, as is known in the art.

Reader 32 and processing unit 36 may communicate using any suitablewired or wireless connection means. Although system 20 can be used inany RFID application, the methods and devices described below areparticularly suitable for RFID applications that require a relativelylong range between transponder 28 and reader 32. In addition, system 20can be used in a variety of challenging environments, such asenvironments in which the communication path between the transponder andthe reader is obstructed by materials such as oil, liquids and metals.

Transponder 28 as described herein is a battery-assisted backscatterRFID transponder. The term “backscatter transponder” means that theresponse radiation is generated by a backscattering effect, in whichpart of the RF energy of the interrogation radiation is reflected fromthe transponder antenna back to the reader. Further, transponder 28 doesnot draw current from an internal battery for generating the RF energyrequired for transmitting the backscattered radiation, thus extendingthe lifetime of the battery and of the transponder.

The term “battery-assisted transponder” (sometimes also referred to as a“semi-active” or a “semi-passive” transponder) means that power requiredto run transponder 28 is derived from an internal power source, such asa battery. In contrast, a passive transponder does not make use of aninternal power source. The energy for powering the transponder circuitryin a passive transponder is derived from the interrogation radiation,which effectively reduces the communication range.

Other transponders, referred to as “active transponders,” use the powerof the internal battery for generating the response radiation. Whilethis configuration may extend the communication range of thetransponder, the power consumption of an active transponder issignificantly higher in comparison to a battery-assisted transponder.The higher power consumption typically means that an active transpondermay either have a significantly shorter lifetime, or have asignificantly larger size to allow for a larger battery. A largerbattery also adds to the cost of the transponder.

The background art has described semi-active transponders, in which someof the energy of the interrogation radiation received by the antenna istransferred to the transponder, absorbed or otherwise made unavailablefor backscattering. Since such a configuration reduces the energy thatis available for backscattering, the communication range of thetransponder is reduced accordingly. However, in embodiments describedherein, the control circuitry of the transponder is powered exclusivelyby the internal battery. As long as the battery is able to supply therequired energy, the energy of the interrogation radiation is not usedto power the transponder. Substantially all of the energy of theinterrogation radiation received by the antenna is thus available forbackscattering. Therefore, the configuration described herein maximizesthe backscatter communication range between the transponder and thereader.

Transponder 28 can take the form of a tag or a label that is attached tothe tracked object. Alternatively, in some cases the transponder may beincorporated as part of the tracked object itself. In other cases thetransponder can be embedded inside a smart-card. Further alternatively,the transponder can be formed and packaged in any other suitableconfiguration, as required by its functionality in system 20. Anexemplary mechanical configuration, in which transponder 28 is formed asa flexible label, is shown in FIG. 8 below. Transponder 28 can beproduced at low cost and thus may be disposable.

In some embodiments, transponder 28 is configured to operate at atemperature range of from about −20° C. to about 65° C. and anon-condensing humidity range of from about 5% to about 95%. In someembodiments, transponder 28 is resistant to liquids and othernon-corrosive materials. In some embodiments, transponder 28 facilitatesimproved communication compared to passive transponders in the presenceof RF absorptive and reflective materials.

The code stored in transponder 28 may conform to any suitable structure,standard or convention. For example, the code may comply with theElectronic Product Code™, an industry-driven standard developed byEPCglobal, Inc. Further details regarding this standard can be found atwww.epcglobalinc.org. An exemplary product identification convention isthe EAN.UCC standard. Details regarding this standard are available atwww.ean-ucc.org. In some embodiments, reader 32 may write input datainto transponder 28 in addition to reading the code, as part of theinterrogation process. The written data can later be read by the samereader or by a different reader in subsequent interrogations.

In some embodiments, the interrogation radiation and the backscatteredradiation are transmitted in the ultra-high frequency (UHF) range,typically between about 300 and about 3000 MHz, although other suitablehigher or lower frequency ranges, such as for example microwaves canalso be used. Nothing herein is meant to limit the invention disclosedherein to operation within the UHF band. The particular choice offrequencies may depend upon national spectrum allocation and otherregulatory and functional constraints. For example, typical frequencyranges are in the range of about 800-900 MHz in Europe and in the rangeof about 900-950 MHz in North America. In some embodiments, the sametransponder can be configured to be operable in different frequencybands depending on geography. As such, the present invention readilyfacilitates seamless operation across the globe.

When reader 32 transmits information or other commands to thetransponder, the transmission can use any suitable modulation type, suchas amplitude shift keying (ASK), frequency shift keying (FSK), singlesideband (SSB), double sideband (DSB) and phase shift keying (PSK)modulation.

FIG. 2 is a block diagram that schematically illustrates details of RFIDsystem 20, in accordance with an embodiment of the present invention.Transponder 28 comprises a substrate 48, which serves as the base formounting the various transponder components. An antenna 52 receives andbackscatters the interrogation radiation transmitted by reader 32. Insome embodiments, the transponder may comprise two or more antennas forimproved coverage.

An integrated circuit (IC) 56, typically an application-specific IC(ASIC), performs the various processing and logic functions oftransponder 28. In some embodiments, some functions of IC 56 areimplemented using discrete components that are disposed on substrate 48as part of the transponder production process.

IC 56 is powered by a battery 60. The RF energy of the interrogationradiation is typically detected, amplified, filtered and demodulated bya detector/demodulator 62 in IC 56. Detector/demodulator 62 detects thepresence of the interrogation radiation and demodulates theinterrogation data, if such data is transmitted by reader 32.Detector/demodulator 62 may use constant false alarm rate (CFAR)techniques known in the art, or any other suitable method, for detectingthe presence of the interrogation radiation in the presence of clutter,background noise and/or interference. In some embodiments, the detectorand demodulator may be integrally formed in one circuit. Alternatively,the detector and demodulator may use separate components or may sharesome components.

A control module 64 typically receives an indication regarding thepresence of the interrogation radiation, and optionally the demodulatedinterrogation data, from detector/demodulator 62. Control module 64retrieves the transponder code, as defined above, which has beenpreviously stored in a memory 66, and sends the code to a modulator 68,which accordingly modulates the RF radiation that is backscattered fromantenna 52 to reader 32.

Battery 60 may comprise one or more suitable energy sources. The batterymay optionally include circuitry configured to increase or otherwisecontrol the supplied voltage. In some embodiments, battery 60 comprisesat least one thin and flexible battery, such as the batteries producedby Power Paper Ltd. (Petah-Tikva, Israel). Such thin and flexiblebatteries are described, for example, in U.S. Pat. Nos. 5,652,043,5,897,522 and 5,811,204, whose disclosures are incorporated herein byreference. Additional details can also be found at www.powerpaper.com.Thin batteries of this sort are typically less than 1 mm thick.

In some embodiments, the transponder is typically less than 1 mm thickand has a bending radius of less than 25 mm. In some embodiments, thetransponder is less than 0.6 mm thick. In some embodiments, thetransponder had a bending radius of less than 50 mm.

In some embodiments, the thin and flexible battery comprises a firstinsoluble negative electrode, a second insoluble positive electrode, andan aqueous electrolyte being disposed between the negative electrode andpositive electrode. The electrolyte layer typically comprises (a) adeliquescent material for keeping the open cell wet at all times; (b) anelectroactive soluble material for obtaining required ionicconductivity; and (c) a water-soluble polymer for obtaining a requiredviscosity for adhering the electrolyte to the electrodes. In someembodiments, the two electrode layers and the electrolyte layer aretypically arranged in a co-facial configuration. Alternatively, the twoelectrode layers and the electrolyte layer can also be arranged in aco-planar configuration. The resulting battery can facilitate an eventhinner transponder.

In other embodiments, battery 60 comprises a thin and flexible batteryas described in US Patent Application Publication 20030165744 A1, whosedisclosure is incorporated herein by reference.

In some embodiments, as described in detail hereinbelow, when battery 60is a thin and flexible battery as described above, the different layersof the battery are deposited on substrate 48 as part of the transponderproduction process. In alternative embodiments, a previously assembledthin and flexible battery is applied or attached to substrate 48.

In some embodiments, battery 60 may be kept in an inactivated state inorder to increase the longevity of the battery. Such a case may bedesirable for a transponder 28, which has been manufactured, but is notyet in use. Any suitable method of facilitating an inactivated state maybe used, such as but not limited to use of a tab over the battery.

In some embodiments, control module 64 comprises a microcontroller corethat runs suitable software, coupled with peripheral logic and memory.Alternatively or additionally, control module 64 may comprise logicalfunctions and management functions implemented in hardware as part of IC56. Memory 66 may comprise any suitable non-volatile or battery-backedmemory, such as an electronically erasable programmable read only memory(E²PROM). Battery-backed memory is sometimes advantageous due to its lowworking voltage and current and low cost.

In some embodiments, memory 66 comprises a read memory section 67, inwhich module 64 stores the code and reads it during its transmission tothe reader, and a write memory section 69, which is used for storingdata sent to the transponder from the reader. In some embodiments, theread and write memory sections can be activated and deactivatedindependently as appropriate, in order to reduce the energy drawn frombattery 60.

In some embodiments, the code is written permanently into memory 66 aspart of the IC fabrication process or as part of the transponderproduction process. In other embodiments, the code can be written andmodified by reader 32 during operation. In some embodiments, writing thecode into the memory requires the use of a password or a suitablesecurity code. The modulator modulates the retrieved code onto thebackscattered radiation, which is backscattered from antenna 52 toreader 32. The modulation method is described in detail hereinbelow.

In some embodiments, transponder 28 comprises authentication and/orencryption means, for verifying the identity of the transponder and/orof the tracked object to the reader.

IC 56 may also comprise an energy saving module 70. Module 70 enablesand disables different hardware functions and components of transponder28, in accordance with the transponder's mode of operation, so as tominimize the current drawn from battery 60 and extend its lifetime.Module 70 can use a battery status indicator 72 for assessing the statusof battery 60. Module 70 is typically implemented as a state-machineusing hardware, software or a combination of both. The operation ofmodule 70 is shown in detail in FIGS. 6A, 6B and 7 below.

In some embodiments, IC 56 comprises a real-time clock (RTC) 74. In someembodiments, the transponder reads the RTC and adds a time-stamp to thecode sent to the reader. In some embodiments, transponder 28 senses oneor more local conditions using one or more external sensors 78. Forexample, sensors 78 may sense the temperature or other environmentalconditions in the vicinity of transponder 28. Sensors 78 may alsocomprise motion sensors, tamper sensors, shock/vibration sensors,humidity sensors, radiation sensors, chemical sensors, gas or fumesensors, weight sensors, drug (narcotics) sensors, explosives sensors orany other suitable sensor.

Some of sensors 78 may have digital or discrete outputs, whereas othersensors may have analog outputs. In some embodiments, IC 56 comprises ananalog to digital converter (ADC) 76 that samples the outputs of theanalog sensors and provides the sampled values to control module 64. Insome cases, at least one sensor, such as a temperature sensor, can beimplemented internally to the IC. In some embodiments, at least onesensor can be implemented externally to IC 56.

In some embodiments, the information of sensors 78 and RTC 74 iscombined to provide time-dependent alarm conditions. For example, IC 56may report an alarm to the reader if the local temperature exceeds apredetermined threshold for a predetermined time duration. The reportedalarm can also contain a time-stamp indicating the time of the event. Insome embodiments, the profile of the sensor measurements over time canbe recorded in memory 66 while the tracked object is outside the readercommunication range. A sensor profile such as a time-temperature profileis important in applications such as fresh food packages, medicalsupplies, drugs and any other temperature-sensitive commodity. In someembodiments, control module 64 can also activate, deactivate orotherwise control parts of the tracked object in accordance withcommands received from the reader.

Transponder 28 can optionally comprise a display, such as, but notlimited to a light-emitting diode (LED) or a liquid crystal display(LCD), not shown in the figures. The display may comprise an indicatorelement, such as, but not limited to a color changing element. In onenon-limiting example, the indicator may readily facilitate a colorchange in the event of a product being out of date or if environmentalconditions such as temperature have exceeded a specified limit.

In some embodiments, the IC comprises a power-on-reset (POR) andwatchdog timer (WD) module 80. The POR typically resets control module64 when power is applied. The watchdog timer typically resets amicrocontroller in control module 64, when such a microcontroller isused, in certain software failure scenarios.

In some embodiments, the functions of IC 56 can also be performed by twoor more application-specific or general-purpose components.

FIGS. 3A-3C are diagrams that schematically illustrate differentexemplary implementations of antenna 52, in accordance with embodimentsof the present invention. Typically, the type of antenna chosen, as wellas its configuration and dimensions, are dependent upon the operatingfrequency and upon the desired size and shape of the transponder.Antenna 52 may comprise a monopole, a dipole, a patch, an array, or anyother suitable antenna type, as appropriate for the specificconfiguration of transponder 28. In some embodiments, parts of theantenna may be bent or otherwise oriented to fit within the allocatedspace on substrate 48.

FIG. 3A shows an exemplary dipole antenna 90 comprising two elementshaving bent tips that are fed at a feed-point 92. In this embodiment,which is optimized to give maximal backscatter and maximal modulationdepth at a frequency of 900 MHz, each element is 102 mm long, of which42 mm are bent at a 90° angle. In an alternative exemplary embodiment,also optimized to operate at 900 MHz, the total length of each elementis still 102 mm, but the bent section is longer, such as 67 mm. Inalternative embodiments, different total lengths and different lengthsof bent tips can be used to suit the desired transponder size. Astraight dipole with no bent tips can also be used if sufficient lengthis available on substrate 48.

FIG. 3B shows an exemplary monopole antenna comprising an active element94 and a ground plane 96. Feed-point 92 is located at the bottom of theactive element, between element 94 and ground plane 96. The total lengthof element 94 is again 102 mm, to maximize backscatter and modulationdepth at the operating frequency of 900 MHz. As with dipole antenna 90,the tip of active element 94 of the monopole antenna is seen to be bent,to fit within the allocated geometry of transponder 28. Differentamounts of bending, and in particular a straight monopole withoutbending, can also be used if sufficient length is available.

Antenna 52 may be deposited on substrate 48 using any suitable method,such as a thick-film deposition method, a printed circuit board (PCB)production method, an etching process, by printing anelectrically-conductive ink, using a metallic foil, using a vaporizationmethod, or using any other suitable method known in the art.

FIG. 3C shows an alternative configuration of transponder 28, in whichthe components of transponder 28 are located on two different surfacesof package 24. In some practical cases, it is desirable to locateantenna 52 on a narrow surface 97 of the package (or other object) thatis too narrow to fit the entire transponder. For example, a surface 98,although wide enough for fitting the transponder, is sometimes made of ametallic material that interferes with the radiation pattern of antenna52. Two such exemplary cases are compact disk (CD) packages and somemedication packages. In another case, the tracked object may not includeany surface wide enough to fit the entire transponder.

In these cases, transponder 28 can be mounted so as to wrap around acorner of package 24. The transponder is thus attached to two differentsurfaces of the package, as shown in the figure. As will be shown below,substrate 48 and the other layers of transponder 28, including antenna52 and battery 60 are typically flexible enough to be wrapped around thecorner in the manner shown or in any other suitable manner, which canfacilitate an improved radiation pattern. In the example of FIG. 3C,antenna 52, in this case a straight dipole antenna, is located on narrowsurface 97 together with IC 56. Battery 60 is located on surface 98 andinterconnected to the IC. In other embodiments, the IC may be separatefrom the antenna and located on the same surface as the battery.

In some embodiments, part of the tracked object can be made from asuitable material, which can function as antenna 52 or part thereof. Inone non-limiting example, part of a metallic crate, to which transponder28 is attached, can be used as a radiating element or as a ground planeof the antenna.

When designing antenna 52 of transponder 28, it is typically desirablethat the antenna radiation pattern be as close as possible to aspherical pattern. A spherical radiation pattern enables the reader tocommunicate with the transponder from any direction, within thespecified communication range. In some embodiments, antenna 52 isorientation insensitive, such that it can operate in any positionrelative to the direction of the reader antenna. Nulls in the antennaradiation pattern typically cause “dead angles,” in which thecommunication range between the reader and the transponder issignificantly reduced. In some embodiments, antenna 52 is optimized toprovide a maximum RCS and a maximum modulation depth (ARCS) duringbackscatter modulation, as described hereinbelow.

FIG. 4A is a diagram that schematically illustrates a 3-D radiationpattern 100 of antenna 52, in accordance with an embodiment of thepresent invention. The figure plots the radiation pattern of themonopole antenna illustrated in FIG. 3B above. For each angulardirection in 3-D space, the plot shows the achievable reading rangebetween reader 32 and transponder 28. In many practical implementations,a true spherical radiation pattern is difficult to achieve and oftenresults in a significant loss of gain. In some embodiments, adoughnut-shaped pattern, such as pattern 100, is typically considered agood approximation.

FIG. 4B is a graph that schematically illustrates coverage of themonopole antenna, in accordance with an embodiment of the presentinvention. A plot 102 shows the percentage of 3-D angles that arecovered by the radiation pattern of FIG. 4A, per each communicationrange. For example, at a communication range of 6.7 m, 95% of the 3-Dangles are covered. In other words, when the distance between reader 32and transponder 28 is 6.7 meters, communication will be available at 95%of the possible reader directions. At a distance of 19.3 meters,approximately 30% of the directions are covered.

Backscatter Modulation

Transponder 28 uses backscatter modulation for modulating the code ontothe backscattered radiation transmitted to the reader. The ratio betweenthe total RF power (of the interrogation radiation) irradiated ontoantenna 52 and the total RF power that is backscattered from antenna 52is referred to as the Radar Cross-Section (RCS) of antenna 52.

Modulator 68 of transponder 28 may receive from control module 64 aserial binary sequence, representing the information that is intended tobe transmitted to the reader. The modulator modulates the RCS of antenna52 responsively to this binary sequence. As a result, the amplitude ofthe backscattered radiation is modulated accordingly. Any suitable bitrate can be used when modulating the antenna RCS. For example, theEPCglobal specification cited above defines bit rates in the range of40-640 kbps for the link from the transponder to the reader. Otherapplications use lower bit rates, in the range of about 1-3 kbps.Alternatively, any other suitable bit rate can be used.

As will be explained in detail below, control module 64 and modulator 68are typically inactivated when interrogation radiation is not sensed bythe transponder. In particular, backscatter modulation is performed onlywhen the interrogation radiation is present. Reader 32 receives thebackscatter-modulated radiation, demodulates and extracts the code, andforwards the information to processing unit 36.

Typically, modulator 68 switches the RCS between two values, referred toas “RCS high” and “RCS low,” corresponding to the 1's and 0's of thebinary sequence that represents the code. Typically, modulator 68 usesbinary amplitude shift keying (ASK) to modulate the value of the antennaRCS. In alternative embodiments, the modulator can modulate the antennaRCS with more than two values, such as using quaternary-ASK modulation.

When transponder 28 performs backscatter modulation, only the energy ofthe interrogation radiation is used for generating the backscatteredradiation. In particular, transponder 28 uses the electrical power ofbattery 60 merely for modulating the antenna RCS, and not for generatingthe energy required for backscattering, thus extending the lifetime ofthe battery and of the transponder.

Typically, modulator 68 varies the RCS of antenna 52 by varying theimpedance at feed-point 92. A first impedance value is set, so that theamount of power that is backscattered from the antenna is minimized,thus providing the “RCS low” state. A second impedance value is set, soas to maximize the power that is backscattered by the antenna, therebyproducing the “RCS high” state. In one embodiment, the modulatorprovides the “RCS high” state by producing an open circuit at theantenna terminals. The open circuit condition causes substantially allof the power of the interrogation radiation received by the antenna tobe backscattered. Therefore, the communication range between thetransponder and the reader is maximized.

Controlling the impedance at the feed-point of antenna 52 enables themodulator to control the absolute RCS values of the antenna, as well asthe ratio between “RCS high” and “RCS low” values. This ratio is denotedARCS, sometimes also referred to as the modulation depth.

In some embodiments, the antenna and the modulator are jointly designedso as to comply with two conditions simultaneously. Maximizing theamount of backscattered power (also referred to as a “backscatter gain”or “backscatter value”) in the “RCS high” state causes a maximization ofthe transponder communication range. At the same time, maximization ofthe modulation depth (ΔRCS) enables the reader to differentiate betweentransmitted 1's and O's, so as to reliably demodulate the code from thebackscattered radiation. Typically, the antenna can be optimized formaximum RCS and ARCS only within the geometrical constraints andavailable size in transponder 28.

In some passive and battery-assisted transponders described in thebackground art that use interrogation radiation power for operating thetransponder, the circuitry that interfaces to the antenna also comprisesmeans for rectifying or otherwise drawing energy from the interrogationradiation. In other words, the antenna is loaded by the transponderpower supply or energy conversion circuitry. Such energy conversioncircuitry typically introduces additional parallel resistance andcapacitance across the antenna, which significantly reduce the antenna'sbackscattering performance. Transponder 28, on the other hand, does notdraw power from antenna 52 for powering the IC. Therefore, antenna 52and its matching can be optimized for maximum backscattering efficiencyand modulation depth without such additional constraints.

In some embodiments, the backscattering efficiency of transponder 28 istypically higher than 75%, and in many cases higher than 95%. Thebackscattering efficiency is defined as the ratio between the totalpower that is backscattered from the antenna and the total power of theinterrogation radiation that is received by the antenna. In other words,a backscattering efficiency of 95% means that 5% of the power of theinterrogation radiation received by the antenna is unavailable forbackscattering, and 95% of the received power is backscattered.

In some embodiments, the modulator comprises a solid-state switch, whichis operatively coupled to the antenna terminals, typically at or nearfeed point 92. The switch changes the value of the impedance that loadsantenna 52 at the antenna feed-point, thus modulating the RCS of theantenna, as explained above.

Switch 82 may comprise a field-effect transistor (FET), aGallium-Arsenide switch, a PIN-diode switch, or a switch produced usingany other suitable switching technology. The switching time of theswitch is typically below 50 ns. In some cases, a high RCS can beproduced by making the input impedance of the IC a low real load (i.e.,a low resistance). A low RCS can typically be obtained by loading theantenna with a real (resistive) load that is matched to the impedance ofthe antenna. It should be noted, however, that the physical size of theantenna has a major effect on the achievable RCS values. Exemplaryimpedance values for switch 82 are as follows: RCS high RCS lowResistance ≦10 Ω ≧1000 Ω Parallel capacitance ≦1 pF ≦0.25 pF

Assuming a half-wavelength antenna, such impedance values cause “RCShigh” and “RCS low” values of approximately −1 dB and approximately −20dB, respectively. Alternatively, any other suitable impedance values canbe used.

Considering the radiation pattern of antenna 52, the “RCS high” and “RCSlow” backscatter modulation states cause antenna 52 to have twodifferent backscatter values in any angular direction. The communicationrange between transponder 28 and reader 32 typically varies with theazimuth and elevation angle of the reader relative to the transponderantenna.

FIGS. 5A-5C are graphs that schematically illustrate “RCS high” and “RCSlow” backscatter values of RFID transponder antennas as a function offrequency, in accordance with embodiments of the present invention. FIG.5A shows the backscatter values of bent dipole antenna 90 shown in FIG.3A above (with 42 mm bent tips). A plot 106 shows the backscatter valueof dipole 90 in the “RCS high” state, plotted as a function offrequency. The backscatter value is expressed in dBi, or dB compared toan ideal isotropic radiator. A plot 108 shows the backscatter value ofthe same dipole antenna, when switched to the “RCS low” state by themodulator. In examining plot 106 it can be seen that the antenna and itsmatching are designed so that the backscatter gain in the “RCS high”state is maximized at the operating frequency of 900 MHz, beingapproximately −7.5 dB. In plots 106 and 108 it can be seen that ARCS(the difference between the values of plot 106 and plot 108 at aparticular frequency) is also maximized at 900 MHz, being approximately4 dB.

FIG. 5B shows the backscatter value of bent dipole antenna 90 with 67 mmbent tips. A plot 110 shows the backscatter value of the antenna in the“RCS high” state, and a plot 112 shows the backscatter value in the “RCSlow” state. Again, the gains are plotted as a function of frequency andexpressed in dBi. As in FIG. 5A, it can be seen that the backscattervalue in the “RCS high” state is maximized at 900 MHz, beingapproximately −12 dB. The value of ΔRCS is also maximized at 900 MHz,being approximately 6 dB.

FIG. 5C shows the backscatter value of the monopole antenna shown inFIG. 3B above. A plot 114 shows the backscatter value of the monopoleantenna in the “RCS high” state, and a plot 116 shows the backscattervalue in the “RCS low” state. Both ARCS and the backscatter value in the“RCS high” state are maximized at 900 MHz, being approximately −8 dBiand 7.5 dB, respectively.

Operational Modes and Energy Saving

FIGS. 6A and 6B are flow charts that schematically illustrate methodsfor communicating between reader 32 and RFID transponder 28, inaccordance with embodiments of the present invention. Transponder 28, aspart of RFID system 20, can operate in various operating modes andsequences. The operating modes may be defined, for example, by theparticular protocol or standard used by system 20, such as the EPCglobalstandard cited above. The specific set of operating modes used bytransponder 28, as well as the various triggers or conditions fortransitions between modes, are typically defined in control module 64and in energy saving module 70 in IC 56.

Although FIGS. 6A and 6B below describe two possible sets of operatingmodes, these are shown purely as clarifying examples. Many other modedefinitions and sequences can be implemented in transponder 28 and insystem 20 in general. Such definitions will be apparent to those skilledin the art and are considered to be within the scope of the presentinvention. In particular, FIGS. 6A and 6B serve to demonstrate theoperation of energy saving module 70 in IC 56. For each operating modedefined for transponder 28, module 70 activates only the requiredhardware functions of transponder 28, so as to minimize the currentdrawn from battery 60.

Energy saving module 70 also comprises timeout timers that determinemaximum time durations that the transponder is allowed to stay in foreach operational mode. These timers typically expire under abnormaloperating conditions, such as when communication failures occur.Typically, when a timeout condition expires, the transponder returns toa “sleep mode,” which consumes little current from battery 60. The useof timeout conditions thus further extends the lifetime of battery 60.The timeout mechanisms can be implemented in hardware, software or acombination of both. Since in some operational modes control module 64is disabled, timeouts that are associated with such operational modesare typically implemented in hardware.

Generally speaking, transponder 28 and reader 32 can be operated in twodifferent regimes or protocols, referred to as Transponder-Talks-First(TTF) and Reader-Talks-First (RTF). In TTF operation, when thetransponder senses the presence of the interrogation radiation, itbegins to transmit its code, typically at random intervals. In RTFoperation (sometimes referred to as Interrogator-Talks-First, or ITF),the reader has to explicitly instruct the transponder to transmit itscode, as part of the interrogation process.

FIG. 6A shows a method that is typical of TTF operation. The methodbegins with transponder 28 in a “sleep mode,” at a standby step 120. Thetransponder continually checks for the presence of interrogationradiation, at a detection step 118 and a reader detection step 119.Until such presence is detected, the transponder remains in sleep mode.Typically, when in sleep mode, energy saving module 70 activates onlyminimal hardware functions and draws minimal current from battery 60.For details regarding the different energy saving states and theoperation of module 70, see FIG. 7 below. In some embodiments, in whichthe transponder comprises RTC 74, RTC 74 can be energized at all timesby the transponder battery, even when the transponder is in sleep mode.

In some embodiments, the RF detector in detector/demodulator 62 isconfigured to distinguish between noise and TEM radiation. By detection,distinction and level measurement of noise and signal, the RF detectorcan readily facilitate changing its detection sensitivity accordingly,such as changing a signal detection reference level in relation to thenoise. As such, the RF detector ensures that the device will not beoperated by the noise and avoids unnecessary drawing of energy frombattery 60.

When interrogation radiation is detected at step 119, the transpondercan enter a semi-active mode, at a semi active operation step 121. Thetransponder can check whether a semi-active timeout expires, at asemi-active expiry step 122. If the timeout expires, the transponder canreturn to sleep mode at step 120.

After entering the semi-active mode, the transponder can activate readmemory section 67 in memory 66, at a read activation step 123. The readmemory is activated to allow the transponder to read its code frommemory 66. The transponder can read the code from memory 66 and cantransmit it to the reader using backscatter modulation, at a codetransmission step 124. Typically, the transponder repeats transmittingthe code at random or pseudo random intervals, to avoid collision withtransmissions from other transponders. Alternatively, any other suitableanti-collision protocol may be adopted by the transponder. Module 70comprises a code transmission timeout counter that determines themaximum time interval or the maximum number of repetitions fortransmitting the code. Once the code transmission timeout expires, thetransponder can return to sleep mode at step 120.

After transmitting its code to the reader, the transponder can check forincoming interrogation data from the reader, at a data checking step125. If such data exists, the transponder can receive the interrogationdata, at an interrogation reception step 126. The interrogation data maycomprise incoming data to be written to memory 66, or commands affectingthe operation of the transponder.

The transponder can check whether the interrogation data comprises a “goto sleep” command, at a sleep checking step 127. If instructed to go tosleep, the transponder can return to step 120. The transponder can checkwhether the interrogation data comprises a message acknowledging thereception (ACK) of the code by the reader and completion of thetransponder's function (also referred to as an “ID validated” message),at a code validation checking step 128. If such a command is received,the transponder can continue to decode the interrogation data at step126.

Otherwise, the transponder can check whether the interrogation datacomprises a “write” command, at a write checking step 129. If a writecommand is detected, and a write mode timeout is not expired, thetransponder can activate write memory section 69 in memory 66, at awrite activation step 132. The transponder can check for subsequent datatransmitted from the reader, at a data checking step 130. If such datais received, the transponder can write the data into memory 66, at awriting step 133. Then, the transponder can return to sleep mode at step120. The write mode timeout timer, checked at a write mode checking step131, can limit the write mode duration in case of communication failure.

If no data is detected, the transponder can return to step 124 and cancontinue to transmit its code and check for data or commands, until thesemi-active mode timeout at module 70 expires. Then, the transponder canreturn to sleep mode at step 120.

FIG. 6B shows an alternative method, which is typical of RTF operation.A basic difference between TTF and RTF operation is that in RTF, oncethe presence of a reader has been detected, the transponder begins tolisten to the reader and check for data or commands.

The method begins with transponder 28 in “sleep mode,” at standby step120. Once a reader is detected at reader detection step 119, thetransponder can enter the semi-active mode at semi-active operation step121. If the semi-active mode timeout expires, as checked by semi-activeexpiry step 122, the transponder can return to sleep mode at step 120.

Otherwise, the transponder can begin to receive and decode theinterrogation data transmitted by the reader, at a decoding step 134. Ifthe received interrogation data comprises a “go to sleep” command, aschecked by a sleep checking step 135, the transponder can return tosleep mode at step 120. Otherwise, the transponder can check whether theinterrogation data comprises a “read” command, at a read checking step136. If a “read” command is received, the transponder can check whetherthe read command is addressed to it, or to its group, at an addresschecking step 137. If the received “read” command is not addressed tothe specific transponder 28 or its group, it can return to decoding step134 and can continue to decode the interrogation data.

If the “read” command is appropriately addressed to the specifictransponder or to its group, the transponder can verify that a read modetimeout in module 70 is not expired, at a read mode expiry checking step138. If expired, the transponder can return to sleep mode at step 120.Otherwise, the transponder can activate read memory section 67 of memory66 and can read the code from it, at a reading step 139. The transpondercan then transmit the code using backscatter modulation to the reader,at a code transmission step 140. Following sending the code, thetransponder can return to step 134 and can continue to decode theincoming interrogation data.

The transponder can check whether the interrogation data comprises anacknowledgement (an “ID received and validated”) message, at avalidation checking step 141. If such a command is received, thetransponder can continue to decode the interrogation data at step 134.

The transponder can then check whether the interrogation data comprisesa “write” command, at a write checking step 142. If a write command isdetected, and a write mode timeout is not expired, the transponder canactivate write memory section 69 in memory 66, at a write activationstep 144. The transponder can check for subsequent data transmitted fromthe reader, at a data checking step 146. If such data is received, thetransponder can write the data into memory 66, at a writing step 145.Then, the transponder can return to sleep mode at step 120. The writemode timeout timer, checked at a write mode checking step 143, can limitthe write mode duration in case of communication failure.

If no data is detected, the transponder can return to step 134 andcontinue to check for and decode the interrogation data, until thesemi-active mode timeout at module 70 expires. Then, the transponder canreturn to sleep mode at step 120.

In some embodiments, IC 56 has a fallback mode of operation, in whichthe transponder can operate similarly to a passive transponder whenbattery 60 is unable to supply sufficient power for powering the IC. Inthese embodiments, the IC can comprise an energy conversion circuit 63comprising a rectifier, a capacitor or similar energy conversion and/orstorage circuitry for drawing energy from the interrogation radiation.IC 56 typically comprises one or more switches for switching energyconversion circuit 63 on and off as needed. (As noted above, the energyconversion circuit typically reduces the backscatter efficiency ofantenna 52. Therefore, it is often desirable to switch the circuit offunder normal battery-assisted operation and use it only when the batteryis not used.)

Energy saving module 70 can check the status of battery 60 using batterystatus indicator 72 and can forward this data to control module 64. Ifindicator 72 senses that the battery has insufficient power, for exampleby sensing that the battery voltage drops below a predeterminedthreshold, module 70 can switch on the energy conversion circuit. Thisfeature enables transponder 28 to continue operating as a passivebackscatter transponder, although typically with a reduced communicationrange, long after battery 60 is exhausted.

FIGS. 6A and 6B show exemplary operational sequences typical of TTF andRTF operation, respectively. In some alternative embodiments, thetransponder can use a unified operational sequence, suitable for bothTTF and RTF operation. In such embodiments, after detecting the presenceof a reader, the transponder typically checks whether the desired modeor operation, as indicated by the reader, is RTF or TTF, and performsthe appropriate operational sequence.

In some embodiments, battery status indicator 130 can include a built intest (BIT) or alternatively BIT can be a separate component. The batterystatus includes, but it not limited to built-in test parameters andbattery low warning. Built-in test parameters can include, but are notlimited to, “battery good” indication, “battery low” indication,“battery needs to be replaced” indication, estimated and calculatednumber of possible operations with battery, and combinations thereof. Insome embodiments, transmission of the battery status is performed withevery transmission of transponder 28, as part of the code.Alternatively, the battery status is transmitted upon request by reader32.

In some scenarios, the interrogation radiation has excess power, abovethe power that is required for reliably communicating with the reader.Such a condition may occur, for example, when the distance between thereader and the transponder is small. In some embodiments, when theinterrogation radiation has excess power, energy conversion circuit 63can draw some or all of the excess power from the interrogationradiation. The transponder may, for example, use the excess power forpowering IC 56 in parallel with battery 60. Additionally oralternatively, the transponder can charge battery 60 using the excesspower. Further additionally or alternatively, the transponder can makeany other suitable use of the excess power of the interrogationradiation.

It should be stressed, however, that when using the power of theinterrogation radiation, first priority is typically given tomaximization of the communication range between the reader and thetransponder at a specified communication reliability. Exploiting theexcess power is thus restricted to cases, in which the transpondercommunication range and communication reliability are not compromised.

Energy Saving In RTF Operation

When transponder 28 operates in RTF mode, as required, for example, bythe EPCglobal standards cited above, there is a particular need forefficient energy saving. The RTF protocol requires the transponder tocontinuously listen and check for data and commands wheneverinterrogation radiation is sensed. Since typical RFID systems containmultiple transponders and sometimes multiple readers, a particulartransponder may sense interrogation radiation for a significantpercentage of the time. The majority of these interrogations aretypically intended for other transponders. If the transponder were tofully activate its circuitry whenever interrogation radiation ispresent, its battery life would be significantly reduced.

Energy saving module 70 in transponder 28 is particularly suitable foroperating in RTF mode and enables a significant extension of thelifetime of battery 60. In principle, once interrogation radiation issensed by the transponder, the transponder analyzes the radiation inorder to determine whether or not the radiation is relevant to it.Module 70 progressively activates components of the transponder, so thatonly the minimal current is drawn from battery 60 during the analysisprocess. Once the radiation is determined to be relevant (e.g., a validinterrogation radiation and not noise or interference, or a radiationaddressed to this specific transponder), module 70 can enable thetransponder to transmit the backscattered radiation or otherwise reactto the interrogation radiation.

In some embodiments, several power saving states are defined in module70. Each operational mode of the transponder, such as the differentmodes described in FIGS. 6A and 6B above, is associated with aparticular energy saving state. Using the different energy savingstates, module 70 activates and deactivates the minimal number ofhardware functions, as required by each operational mode. In anexemplary embodiment, five different power management states are definedin module 70, in accordance with the following table: Energy savingTransponder Typical state Functionality Active hardware current A Checkfor RF detector in <0.25 μA presence of detector/demodulatorinterrogation 62 radiation power B Search for Detector/demodulator <3 μApreamble in 62, preamble interrogation identifier in module radiation 64C Decode Same as in B above, <5 μA interrogation plus a command data andidentifier in module commands 64 D Read mode Same as C above, <10 μA(operate full plus module 64 and logic and read read memory in code frommemory 66 memory) E Write mode Same as D above, <15 μA (operate fullplus write memory in logic and write memory 66 data to memory)

FIG. 7 is a state diagram that schematically illustrates an exemplarymechanism for energy saving, carried out by module 70 in RTF mode, inaccordance with an embodiment of the present invention.

The mechanism of FIG. 7 is invoked when transponder 28 senses thepresence of interrogation radiation. This mechanism can be invoked, forexample, after reader detection step 119 in the method of FIG. 6B aboveand can replace steps 119-134 of this method.

Following detection of the interrogation radiation, transponder 28 cancheck for the existence of a predetermined data pattern in theinterrogation radiation, in a pattern checking state 240. The purpose ofstep 240 is to avoid activating unnecessary hardware components until itis verified that the sensed energy originates from a valid interrogationradiation of a reader and not from noise or interference. In state 240,module 70 is in energy saving state B (as defined in the table above)and the current drawn from battery 60 is typically below 3 μA at 1.5volts. State 240 thus enables screening many false alarm events whiledrawing minimal current from the battery.

Once a valid pattern is detected, transponder 28 can demodulate thepreamble of the interrogation radiation and can check for specificaddressing, in an address verification state 242. The purpose of state242 is to screen out interrogations that are not addressed to thisspecific transponder, and thus should be ignored. In state 242, module70 is in energy saving state C and the current drawn from battery 60 istypically below 5 μA at 1.5 volts. If specific addressing is notdetected within a predetermined timeout interval, the transponder canreturn to state 240.

Once the interrogation is found to be addressed to the specifictransponder, module 70 can activate the hardware necessary fordemodulating the full interrogation data, and can receive the data in aninterrogation demodulation state 244. In state 244, module 70 is inenergy saving state D and the current drawn from battery 60 is typicallybelow 10 μA at 1.5 volts.

As can be appreciated from the mechanism described above, state 244 isreached only when it is assured that a valid interrogation radiationthat is intended for the specific transponder is being received.Therefore, the use of this state machine mechanism reduces significantlythe average current drawn from battery 60 in RTF operation.

In some embodiments, transponder 28 can also change its operational modein response to predetermined timeout conditions. Such conditions areevaluated and activated by energy saving module 70. For example:

If interrogation radiation is detected for a predetermined duration oftime, but within this time duration no pattern is detected, thetransponder can regard the detected energy as noise or interference.Following such an event, module 70 may force the transponder to ignoresubsequent interrogation detections for a predetermined time interval.

If a pattern is detected but no addressing to the specific transponderis detected within a predetermined duration of time, module 70 may forcethe transponder to ignore subsequent interrogation detections for apredetermined time interval.

Following a successful interrogation and data exchange between thetransponder and the reader, the transponder may conclude that the readeris not likely to interrogate it again for a certain period of time. Insuch case, module 70 forces the transponder to ignore subsequentinterrogation detections for a predetermined time interval following asuccessful interrogation. (This condition demonstrates that in somecases, timeout conditions can use knowledge of the specific RTF protocolused, in order to save battery energy.)

By using timeout conditions, the transponder is able to spend a higherpercentage of the time in states that consume less power, thus reducingthe average power consumption from battery 60. Combining the timeoutconditions with the state machine mechanism shown in FIG. 7 above, theaverage current consumption from battery 60 is significantly reduced.The lower energy consumption can be used to extend the lifetime of thetransponder, or to reduce the size of battery 60 and further miniaturizethe transponder.

RFID Transponder Mechanical Structure

FIG. 8 is a schematic exploded view of RFID transponder 28, inaccordance with an embodiment of the present invention. In this example,transponder 28 takes the form of a thin and flexible label. In onenon-limiting example, the label has a size of approximately 3 by 5inches and the label is less than 1 mm thick. The same basic designstructure can be used in different forms and sizes of battery assistedRFID transponders. The upper side of FIG. 8 corresponds to the side ofthe label that is attached to the tracked object.

The figure shows substrate 48, which can optionally be any suitablesubstrate as described hereinabove. In some embodiments, substrate ispolyester, such as but not limited to polyester 75 micron. Antenna 52 isdeposited on substrate 48. The antenna in this example is the monopoleantenna shown in FIG. 3B, which is printed as a metallic layer onsubstrate 48. Both active element 94 and ground plane 96 can be clearlyseen in the figure. In addition to the antenna, the printed metalliclayer comprises conductors that interconnect IC 56 with battery 60 andantenna 52 once they are attached to the substrate. Battery 60, in thiscase a Power Paper® battery type STD-3 or STD-4, is attached in asuitable location on top of ground plane 96. The battery terminals areconnected to the printed conductors by a suitable connection means, suchas by using a suitable electrically-conductive adhesive 185. IC 56 isattached in a suitable location on the substrate and interconnected withthe battery and the antenna.

The substrate and the components mounted on it are attached to a liner186, such as but not limited to a silicone liner, using for example adouble-sided adhesive 187. When attaching transponder 28 to package 24or other tracked object, the silicone liner can be peeled off, and thetransponder attached to the object using the double-sided adhesive.

A front liner 188 is attached to the bottom side of surface 48. In someembodiments, the front liner comprises adhesive polyethylene, a suitabledouble-sided adhesive tape. Alternatively, any other suitable liner canbe used. In some embodiments, a graphic label 189 can be attached to thefront liner. Label 189 may comprise any relevant textual or graphicalinformation, such as a company logo or a bar-code.

In some embodiments, additional layers, such as adhesive layers (notshown in figure) are applied, which are configured to facilitate uniformthickness of the transponder label.

In an alternative embodiment, release liner 186 can be disposed on thedistal side of substrate 48. However, this configuration is not alwayssuitable due to the proximity of antenna 52 to the packaging of thetracked object.

The resulting transponder structure is small, flat and flexible,enabling it to easily attach to different objects and to conform to theshape of the object. In sufficiently large volumes, such label islow-cost and can be disposed of after use.

FIG. 9 is a flow chart that schematically illustrates a method forproducing RFID transponder 28, in accordance with an embodiment of thepresent invention. A substrate 48 is provided, at a substrateprovisioning step 190. Substrate 48 can typically be made of a materialsuch as polyester or paper. Other examples of substrate materialsinclude woven materials, non-woven materials, polymers, conductingmaterials, non-conducting materials, cardboard, plastic, syntheticmaterials, natural materials, fabrics, metals, wood, glass, Perspex, acombination thereof or any other suitable material.

Optionally, substrate 48 can be made up of a plurality of substrate baselayers that are stacked or connected in a co-planar way by any suitableattachment methodology. In an embodiment, in which substrate 48comprises a plurality of base layers, each of the antenna, IC andbattery can optionally be attached to a different substrate base layer.Optionally, substrate 48 can be of any suitable size, shape or color.

In one embodiment, substrate 48 can be made integral with the trackedobject or its packaging. For example, substrate 48 can be made anintegral part of a cardboard box, wooden crate, metal crate, plasticbox, metal can, car, etc. In such a way, transponder 28 can be produceddirectly onto an end-product material, which can then optionally befurther processed to form the tracked object or its packaging. Thisembodiment facilitates an integrated RFID transponder.

In some embodiments, substrate 48 can be implemented to comprise asuitable attachment means, which readily facilitate attachingtransponder 28 to the tracked object or its packaging. The attachmentmeans may comprise but are not limited to, adhesive, self adhesivelabel, hook and loop fastening systems (such as Velcro®), magneticattachment, suction attachment, ties and combinations thereof.

Antenna 52 is deposited onto substrate 48, at an antenna deposition step192. The antenna may be deposited using a thick-film deposition method,an etching process, by attaching a metallic foil or template cut to theappropriate shape, by printing a suitable electrically-conductive ink,using a vaporization method, or using any other suitable depositionmethod. In some embodiments, antenna 52 is deposited on the substrateusing a suitable printed circuit board (PCB) manufacturing process. Inthese embodiments, substrate 48 comprises a suitable PCB material with ametallic layer disposed thereon.

IC 56 is placed on substrate 48, at an IC placement step 194. The IC maybe soldered, glued or otherwise attached to the substrate using anyother suitable means. In one embodiment, the IC is interconnected withconductors disposed on the substrate using “flip-chip” technology, as isknown in the art. In this embodiment, the flip-chip interconnectionsfunction as the mechanical attachment means as well. The conductors maybe deposited on the substrate together with the antenna at step 192.Typically, the location of the IC is chosen to be as close as possibleto feed point 92 of antenna 52, so as to maintain the desired impedancematch or mismatch and to minimize signal losses.

In an alternative embodiment, IC 56 may comprise an organic polymerelectronic chip, as known in the art. Such a polymer chip is printableand can be printed directly on substrate 48. The use of such a chip canfacilitate production of a fully printable transponder, in which thebattery, connectors, antenna and chip can be printed onto the substrate.

In still a further alternative embodiment, a plurality of discretecomponents can be used instead of IC 56. Such discrete components canpreferably be produced using a printing technology and can be printed onsubstrate 48. The printable discrete components can facilitateproduction of a fully printable transponder.

Battery 60 is applied to substrate 48, at a battery application step196. The battery can be mechanically attached to the substrate at anysuitable location and using any suitable attachment means, such asgluing, crimping or soldering. In some embodiments, the location ofbattery 60 is chosen so as to minimize interference with the radiationpattern of antenna 52. For example, in the mechanical configurationshown in FIG. 8 above, the battery is attached over the area of groundplane 96, so as to minimize the effect on the radiation pattern of themonopole antenna.

In some embodiments, when battery 60 comprises a thin and flexiblebattery such as the Power Paper batteries described above, the differentlayers of battery 60 can be deposited or printed on substrate 48 as anintegral part of the transponder production process. In one exemplaryembodiment, substrate 48 of the transponder serves as the substrate forone of the electrodes of battery 60, and another substrate is used forthe second electrode. An exemplary battery and a method for producingsuch a battery are shown in FIGS. 10A and 10B below. Alternatively, athin and flexible battery can be assembled separately and then attachedto substrate 48.

In one optional embodiment, part of the battery may be used as part ofor in place of antenna 52. For example, the conductive material of oneor both of the battery electrode layers can function as part of theantenna.

Having deposited the antenna, IC and battery on the substrate, the threecomponents are interconnected, at an interconnection step 198.Interconnection of the IC may use any suitable IC interconnection means,such as “flip-chip” methods and wire bonding. Battery 60 can beinterconnected with the other transponder components by directsoldering, using PCB conductors or using any other suitable connectionmeans.

In some embodiments, the transponder is activated and tested as soon asthe antenna, IC and battery are interconnected, at a testing step 200.

Optionally, additional layers are added to the transponder, at apackaging step 202. For example, top and bottom liners can be added inorder to improve the mechanical durability of the transponder and tofacilitate the attachment of the transponder to the tracked object. Insome embodiments, an additional layer is applied underneath substrate48, in order to introduce additional separation between antenna 52 andthe surface of the tracked object. This added separation may be needed,for example, when the tracked object is metallic, for reducinginterference from the tracked object to the radiation pattern of theantenna. In some cases, an external lamination is applied to thetransponder. Additional items such as a bar-code or graphical label canalso be added at this stage.

Optionally, the code is written into memory 66 of the transponder, at anID writing step 204. Alternatively, the code may be pre-programmed intothe memory or stored in the memory at a later stage.

Note that steps 190-204 above can be executed in different orders. Forexample, when battery 60 is fabricated as part of the transponderproduction process, step 196 is inherently simultaneous with step 198.As another example, testing step 200 can also be executed afterpackaging step 202, when the transponder is fully assembled.

In some embodiments, transponder 28 is particularly suitable formanufacturing using a continuous, fully-automated, printing, drying andlaminating process. In some embodiments, a roll-to-roll process, isused. Such a roll-to-roll process is capable of efficientlymass-producing transponders 28. The method described by steps 190-204above can be readily adapted to different transponder configurations andto different manufacturing volumes and technologies.

FIG. 10A is a schematic exploded view of a printed battery, inaccordance with an embodiment of the present invention. The printedbattery of FIG. 10A is a thin and flexible 1.5 V cell, which can be usedas battery 60 of transponder 28. Some of the battery elements areprinted using certain inks having the desired chemical composition.Similar batteries and production methods are also described in detail inU.S. Pat. Nos. 5,652,043, 5,897,522 and 5,811,204 cited above.

In this embodiment, battery 60 comprises two current collectors 205applied to substrates 206. An anode layer 207 is applied to one currentcollector and a cathode layer 208 is applied to the other currentcollector. An electrolyte 209 is applied to anode layer 207, to cathodelayer 208, or to both. A separator layer 210 is inserted between theanode and cathode layers.

FIG. 10B is a flow chart that schematically illustrates an exemplarymethod for producing battery 60 of FIG. 10A, in accordance with anembodiment of the present invention. The method described below can beused to implement battery application step 196 of the transponderproduction method of FIG. 9 above. In some embodiments, the battery ismanufactured separately and then integrated into the transponder. Inother embodiments, the battery is printed and fabricated on the samesubstrate as transponder 28, as an integral part of the transponderproduction method.

The method comprises printing current collectors 205, at a currentcollector printing step 211. Typically, two current collectors areprinted, one for collecting the anode current and one for collecting thecathode current. The collectors are printed on suitable substrates 206,such as polyester substrates. (When the battery is printed as part ofthe transponder production process, substrate 48 of the transponder canserve as one of substrates 206.) In some embodiments, the currentcollectors comprise a layer of current collector ink, for exampleCurrent Collector Ink 2501, P/N 0002.25.01, produced by Power Paper Ltd.The current collectors are typically dried after printing using suitabledrying means, such as an oven.

Anode layer 207 and cathode layer 208 are printed on top of the currentcollectors, at an electrode printing step 212. Anode layer 207 typicallycomprises a suitable anode ink, for example a zinc anode ink such asAnode Ink 2101, P/N 0002.21.01, produced by Power Paper Ltd. Cathodelayer 208 typically comprises a suitable cathode ink, for example amanganese dioxide (MnO₂) ink such as Cathode Ink 2201, P/N 0002.22.01,produced by Power Paper Ltd. After printing, the anode and cathodelayers are typically dried after printing using suitable drying means,such as an oven.

Electrolyte 209 is applied by any suitable means at an electrolyteapplying step 214. The electrolyte can be applied to anode layer 207, tocathode layer 208, or to both. In some embodiments, particularly when astencil printing process is used, electrolyte 209 may comprise anelectrolyte ink such as Electrolyte 2301, P/N 0002.23.01, produced byPower Paper Ltd. In other embodiments, particularly when a screenprinting process is used, electrolyte 209 may comprise an electrolyteink such as SP Electrolyte 2302, P/N 0002.23.02, produced by Power PaperLtd. In some embodiments, electrolyte layer 208 comprises zinc chloride.Alternatively, any other suitable electrolyte material can be used.

Separator layer 210 is placed on top of the electrolyte layer of eitherthe anode layers or cathode layers, at a separator insertion step 216.The separator layer separates the anode layer from the cathode layer,while allowing ion conductivity between the electrodes. Typically, theseparator layer comprises a porous insoluble substance, such as, but notlimited to, filter paper, plastic membrane, cellulose membrane, cloth ornon-woven material (e.g., cotton fibers).

In an alternative embodiment, separator layer 210 can self-form as aresult of a reaction and/or an interaction between materials in the twoelectrolyte layers.

The battery is assembled at a cell assembly step 218. In someembodiments, this step can include applying an adhesive frame, such as apressure sensitive glue frame, which can be applied onto the edge of thesingle cell substrate. This step can further include laminating theelectrode layers with the separator to the opposite electrode layerwithout the separator. In such a way the substrates, current collectors,electrodes, electrolyte and separator layers are stacked in the mannershown in FIG. 10A above. In some embodiments, a press, such as but notlimited to a hot press, is used to press the glue frame for optimaladherence of the glue frame.

In some embodiments, connectors can be attached to the currentcollectors as part of or following the cell assembly step. Theconnectors may comprise, for example, metallic tabs or strips,double-sided conductive adhesive tape and heat-sealed connectors.

Implementation Examples

Reference is now made to the following two examples, which together withthe above descriptions illustrate the invention in a non-limitingfashion. The following table provides an exemplary specification of atransponder 28, in accordance with an embodiment of the presentinvention: Parameter Specification Operating frequency 860-880 and902-928 MHz Frequency hopping operation As authorized for the readerOptimized antenna RCS σ/λ² = 1 m² for a 10 × 10 cm label area Optimizedantenna ΔRCS Δσ/λ² = 0.9 RCS Free space read and write 30 m range withreader effective isotropic radiated power (EIRP) = 4 Watt Reader totransponder ASK, DSB, SSB, FSK or PSK modulation Transponder to readerASK or subcarrier PSK modulation Reader to transponder data 4.8-128kbit/sec rate Transponder to reader data 4.8-512 kbit/sec rate Reader totransponder coding NRZ, Miller, PIE or PWM Transponder to reader codingdirect or subcarrier, NRZ, FM0 or Miller Basic non-volatile (EEPROM)memory organization: UID 64-196 Bits System Memory 128 Bits Passwordsand CRC 64 Bits User Memory 120 Bits Operating temperature −20-+60° C.Non-damaging RF input at the ≦+20 dbm antenna terminal

An exemplary implementation of transponder 28, in the form of a label,was tested in different operating environments. In each environment, thereading reliability (percentage of successful interrogations) andreading range were measured. The following table shows non-limitingexamples of test results for several challenging environments. All testsused a reader 32 having a single antenna. In particular, some of thetest environments included foils and other metallic objects in thevicinity of the transponder. Nevertheless, 100% reading reliability wasachieved in nearly all environments, as can be seen in the table:Reading Reliability Tracked (% of labels Reading Range object Testscenario read) (feet) Metal Outdoor 100% Up to 30 feet containersloading/unloading filled with area fragrance liquid Aluminum foilDistribution 100% 10 feet juice boxes center; reader on truck door; 100boxes on metal roll containers; container- level tagging Canned foodDistribution 100% 10 feet center; reader on truck door; 100 boxes onmetal roll containers; container- level tagging Ice cream (atDistribution 100% 10 feet −30° C.) center; reader on truck door; 100boxes on metal roll containers; container- level tagging Mixed goodsReader/gate 100% 10 feet (e.g., scenario. spaghetti Several sauce,labels in and metallic around boxes coffee on a pallet canisters, spicysauce in aluminum foil) Dishwashing Reader/gate 100% 10 feet detergentscenario. Labels placed around a box holding boxes of detergent Babywipes Labels 100% 10 feet sandwiched in between individual itemsCigarette Item level;  98% N/A packs one label per (aluminum pack; foil)conveyer belt test Beverages Item level; 100% N/A (wine, soda one labelper cans, etc.) bottle/can Oil lubricant Item level on 100% 23-30 feetbottles pallet in several layers Condensed dog Item level 100% 32 feetfood (22 lb. bags) Wooden blocks Multiple tags 100% Up to 40 feetstaggered on three level wood blocks

Although the methods and devices described herein mainly addressbattery-assisted UHF backscatter RFID transponders, the principles ofthe present invention can be used for additional applications, as well.Such applications include, for example, electronic article surveillance(EAS) systems and authentication applications in EAS systems.

It will thus be appreciated that the embodiments described above arecited by way of example, and that the present invention is not limitedto what has been particularly shown and described hereinabove. Rather,the scope of the present invention includes both combinations andsub-combinations of the various features described hereinabove, as wellas variations and modifications thereof which would occur to personsskilled in the art upon reading the foregoing description and which arenot disclosed in the prior art.

1. An antenna for transmitting information from a radio frequency (RF)transponder, wherein the antenna is configured to receive RFinterrogation radiation at a first power level from an interrogationdevice, to backscatter the interrogation radiation at a second powerlevel that is greater than 75% of the first power level, and wherein theantenna has a variable radiation characteristic, which is controllableby the transponder so as to modulate the information onto thebackscattered radiation.
 2. The antenna according to claim 1, whereinthe second power level is greater than 95% of the first power level. 3.The antenna according to claim 1, wherein the antenna is selected fromthe group consisting of at least one of a monopole, a bent monopole, adipole, a bent dipole, a patch, an array antenna and a combinationthereof.
 4. The antenna according to claim 1, wherein the antenna isconfigured to receive and backscatter the interrogation radiation in oneof an ultra-high frequency (UHF) range and a microwave frequency range.5. The antenna according to claim 1, wherein the antenna is configuredto receive and backscatter transverse electromagnetic (TEM) radiation.6. The antenna according to claim 1, wherein the antenna comprises afeed-point, and wherein the radiation characteristic comprises a radarcross-section (RCS) of the antenna, and wherein the antenna iscontrollable to modulate the information responsively to variations of aload impedance at the feed-point of the antenna so as to vary the RCSbetween two or more different RCS values.
 7. The antenna according toclaim 6, wherein the antenna is configured to maximize at least one ofthe two or more RCS values responsively to a low resistive loadcondition applied to the feed-point of the antenna, thereby maximizing acommunication range of the transponder.
 8. The antenna according toclaim 6, wherein the antenna is arranged to maximize a modulation depthdefined as a ratio between two of the two or more RCS values.
 9. Theantenna according to claim 8, wherein the antenna is configured tojointly maximize the modulation depth and a communication range of thetransponder.